If you have a string instrument of any kind that needs fixing, a mistake you made in building a new instrument that you need to "disappear," or a question about the ethics of altering an older instrument, ask here. Please note that it will be much easier for us to help you decide on the best repair method if you post some pictures of the problem.

Stick in 2 playing card thick pieces of paper. You can leave it loose or glue it in.

If you want it to not show, buy a piece of bone from the pet shop, and cut a new nut that is a little thicker. You can also make nuts out of wood (generally the harder the better) corian, and other various materials.

All of these suggestions are valid. It depends on how fussy you are about appearances and how creative you are with things like wooden infills. You could even compromise. Fill it with strips of cards or veneer strips and play it that way until a new, thicker nut blank arrives in the mail. I'm serious.